WASHINGTON — The last photograph that Jennifer Runnion saw of her adopted daughter Isilie was taken in March.

“I have no contact with her right now,” the mother from Amesbury said in a recent interview, her voice breaking. “I am missing milestones in my daughter’s life. She was 5 months old when I first saw her face and now she is over 2 years old.”

The Runnions are among hundreds of American parents-to-be who have legally adopted an orphan from the war-torn Democratic Republic of Congo but have been unable to unite with their child because the African nation stopped issuing exit visas for adopted children nearly a year ago.

As the Runnions’ angst and frustration grow, their case and more than 800 others — including nearly 150 who, on paper, have been granted full legal custody of their adopted child — are garnering attention in Congress. The Senate formally called on Congo to release the children, just days before its leader is set to arrive in Washington for an official visit this week.

At the same time, some child welfare and adoption advocates believe the US State Department could be more aggressive in intervening with countries such as Congo that are slowing the pace of international adoptions, which have dropped dramatically in recent years.

Jennifer and her husband, Timm, are paying $300 a month to an adoption agency to ensure that Isilie is in foster care. While they assume the money is getting to her, they don’t know for sure. And with 1 out of every 7 Congolese children dying before their 5th birthday — from disease, malnutrition, or tribal violence — every day they wait brings new fears for her welfare.

“There is not a day that goes by that I am not thinking ‘is something going to happen to her today?’ ” Jennifer said.

The Runnions began their search in April 2011 for a sibling for their other adopted daughter, Zion, now 7, who was born in Ethiopia. The international adoption agency they hired sent them a referral for Isilie Mukansongo in November 2012. Isilie officially became their daughter in April 2013 after a ruling by a Congolese court. The family subsequently received all the necessary immigration approvals from the American side, including the little girl’s passport in September of 2013 — just as Congo began to curb exit visas.

“We can’t bring her home because the immigration authority in [the Congo] stopped issuing those permits,” explained Jennifer.

The Congolese government, which did not respond to several calls seeking comment, has said in the past that it was putting all international adoptions on hold pending a new adoption law. The new law is needed, Congolese officials said, in order to root out illegal or fraudulent adoptions.

US officials say they share a desire to make sure adoptions are conducted with integrity, while contending it is wrong to hold up adoptions that have already been approved by the Congolese court system, completed their mandated US government review, and for which American entry visas have been issued.

“We do want adoptions to be ethical and transparent,” said a senior State Department official who would speak only on the condition of anonymity, because of the diplomatic sensitivities. “But at the same time . . . if the children are now the responsibility of their American parents, I really do believe that those cases should be able to move forward.”

Mark Lorenz for The Boston Globe

Timm and Jennifer Runnion took a boat ride up the Merrimack River in Amesbury with their daughter, Zion. They long to bring home their other daughter, Isilie.

The Runnions’ experience comes amid what many call an “orphan crisis” in Africa, where there are an estimated 56 million children who have lost at least one parent — enough to collectively make up the fourth-largest country on the vast continent. Their parents have been victims of a deadly mix of civil war, weak health systems, natural disasters, the scourge of HIV/AIDS, and abject poverty.

Despite the high number of orphans and demand from willing parents in the United States, international adoptions overall have plummeted over the last decade by nearly 70 percent, according to State Department statistics. A major cause is reluctance among foreign countries, including Russia and China, to send their orphaned children abroad. There also is an inaccurate impression in some foreign countries that children adopted by Americans are subject to abuse in poverty once they arrive, the State Department official said.

“In many countries, intercountry adoptions can be a very hard sell,” the official said.

Representative Chris Smith, a New Jersey Republican who chairs the House Subcommittee on Africa, Global Human Rights, and International Organizations, has elevated the issue in Congress. The issue of orphans in Africa is not just a humanitarian crisis, he asserted, but one freighted with “strategic implications.”

“We have all heard of the scourge of child soldiers, how orphaned children are recruited and brutalized, themselves turning into remorseless killers,” Smith said at a recent hearing.

The State Department plays a key role in international adoptions, conducting reviews of all adoption cases and issuing visas for adopted children in conjunction with US Citizenship and Immigration Services.

But Kelly Tillotson Dempsey, general counsel of Both Ends Burning, an Arizona-based child welfare group, has been among the fiercest critics. She advocates a much more proactive role for US diplomats, recently calling for “a true sense of urgency in our government’s actions as adoptions are processed.”

The State Department insists it is doing everything it can — especially on the Congo cases, noting that numerous meetings have been held with Congolese officials to plead the case of the Runnions and others.

Indeed, the Obama administration has made some progress. In May, Secretary of State John F. Kerry, during a visit to the Congolese capital of Kinshasa, raised the issue with President Joseph Kabila and later that month 19 children who were awaiting exit visas were cleared, four of whom were considered “medically fragile.”

But earlier this month dozens of senators wrote to President Obama asking him for his “personal engagement” on the issue when his Congolese counterpart arrives in Washington for a summit on Africa hosted by the State Department.

They told him the 19 cases that were resolved “represents only a small percentage of the completed cases and leaves dozens of critically ill children without the medical care they need to survive.”

One of the signatories of the letter is Senator Edward Markey, a Massachusetts Democrat and member of the Foreign Relations Committee.

“They went through the process that was created by the Congolese government,” Markey said of the Runnions and others like them, including another couple from Massachusetts who wishes to remain private. “The families have completed the process.”

He said he believes “the only way the [Congolese government] will grant exit visas is if the US presses them to do so.”

He said he hopes the congressional pressure will “make it easier for Obama to advocate with Kabila when he comes to Washington.”

While they wait, the Runnions’ emotional burden seems particularly acute given how the first experience with international adoption has been so rewarding.

“I have had such a marvelous, unbelievably loving experience with this first adoptive child,” said Timm, 63. “She is like our blood. We’ll say to each other, ‘You sure we didn’t have this kid?’ That doubles the fear when you have a child in another country that you can’t take care of.”

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